1. Field of the Invention:
The present invention relates to a piezoelectric transducer and specifically, the present invention relates to a piezoelectric transducer, a manufacturing method of the piezoelectric transducer and a pulse wave detector for detecting the information of the interior of a human body and the interior of an object.
2. Description of the Prior Art:
A conventional piezoelectric transducer to be used as an ultrasonic probe or the like will be explained with reference to FIGS. 16, 17 and 18.
FIG. 16 is a perspective view of a conventional piezoelectric transducer and FIG. 17 is a side view of the piezoelectric transducer shown in FIG. 16.
A piezoelectric transducer 100 consists of an acoustic matching layer 110, a backing material 130, a piezoelectric element 101 and a flexible substrate 120 for applying a voltage to the piezoelectric element.
The piezoelectric transducer 100 is configured in such a manner that the flexible substrate 120 and the piezoelectric element 101 are attached on the backing material 130 made of a mixture of tungsten powder and an epoxy resin, further, the acoustic matching layer 110 such as a resin is applied or attached on the piezoelectric element 101 and finally, the piezoelectric element 101 is cut into strips by dicing. As shown in FIG. 17, the piezoelectric element 101 is provided with electrodes 102 and 103. The electrode 102 is electrically connected to the flexible substrate 120 via an upper surface 101a of the piezoelectric element, so that the electrode 102 is also electrically connected to the side surfaces of the piezoelectric element 101.
Alternatively, FIG. 18 shows a piezoelectric transducer such that a piezoelectric element is embedded in the resin. On the opposite surfaces of piezoelectric elements 210 and 220, a conducting wire 240 for applying a voltage is bonded with the conductive adhesive or the like to be embedded in a resin 230.
A constitution of the general ultrasonic probe, namely, a general piezoelectric transducer embedded in the resin is as described above.
With respect to the conventional piezoelectric transducer to be used as the ultrasonic probe, it is necessary to apply a special patterning to the piezoelectric element, which involves a problem such that the conventional piezoelectric transducer is difficult to manufacture the manufacturing cost of the conventional constitution is higher.
Alternatively, according to the piezoelectric transducer to be generally used for a living body, the acoustic matching layer made of a resin or the like for efficiently transmitting the ultrasonic wave to the interior of the living body is provided on the upper surface of the piezoelectric element.
The optimum thickness of this acoustic matching layer is around ¼ of a wave length of the ultrasonic wave to be used. If it becomes thicker, the ultrasonic wave is attenuated and as a result, detection sensitivity of the pulse wave or the like is deteriorated. Therefore, in the case of bonding the conducting wire to the piezoelectric element with the conductive adhesive or the like such as the piezoelectric transducer embedded in the resin, it is necessary to make the thickness of the conductive adhesive and the thickness of the conductive wire less than or equal to that of the above mentioned acoustic matching layer, so that it is very difficult to manufacture such a piezoelectric transducer and the thickness of the acoustic matching layer becomes thicker than the optimum thickness. This involves a problem such that the detection sensitivity has been deteriorated.
Additionally, if the conductive wire made of a thick or hard material is used, a vibration property of the piezoelectric element comes under the influence and if the thick conductive wire is used, unnecessary stress and an unnecessary fixed point are generated in the piezoelectric element and a vibration mode comes under the influence. Further, a resonant frequency is deviated and impedance of the resonant frequency is changed, so that it is not possible to effectively vibrate the piezoelectric element. As a result, this involves a problem such that a desired detection sensitivity cannot be obtained.